Abstract
To study compositional dependent conductivity of Li+-ions in lithium perchlorate/poly(ethylene oxide) (LiClO4/PEO) electrolytes, mobility of the Li+-ions and morphology of the electrolytes are investigated by examining the spin-lattice relaxation time (T1) of 7Li and by high-resolution solid-state 13C NMR methods. It is shown that the amount of the mobile Li+-ion estimated from the shorter 7Li-T1 component is not directly compared with the reported conductivity. The high-resolution solid-state 13C NMR spectra show that there exists five different CH2 carbons in the LiClO4/PEO electrolytes. The five peaks are assigned to (1) the crystalline phase of pure PEO, (2) the amorphous phase of PEO with the Li+-ions, and three complex phases of the following ratio of (3) PEO : Li+=3 : 1, (4) x : 1 (3<x<6), and (5) 6 : 1 . Furthermore, it is shown that the domain size of the PEO : Li+=6 : 1 phase in the LiClO4/PEO = 1/6 electrolyte is large and the mobility of the Li+-ions in the phase is so fast as to give a short 7Li-T1 comparable to that in the amorphous phase. The former ions are confined in the PEO : Li+=6 : 1 phase and do not contribute to conductivity while the latter does. Therefore, care should be taken in correlating the amount of the mobile Li+-ions obtained from the 7Li-T1 data to the Li+-ion conductivity.
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